1. Field of the Invention
This invention relates to low temperature-sintering porcelain components and, more particularly, to low temperature-sintering porcelain components suitable for an electric circuit substrate, for example, a multi-layer electric circuit substrate in which a plurality of sheet-form porcelains are laminated and electric circuits are formed on the porcelains.
2. Description of the Prior Art
Heretofore, a multi-layer electric circuit substrate which comprises electric circuit elements such as inductors, capacitors, and resistors in a unified substrate has been developed.
Recently, the multi-layer electric circuit substrate of this type has been increasingly used for applications in a high frequency range, and copper or the like having low resistivity in the high frequency range has attracted attention as a conductor material.
The inventors of this invention have proposed several kinds of porcelain components which can be baked at a low temperature and can produce porcelain having a high insulation resistance and a low dielectric constant. These porcelain components have been disclosed in, for example, Japanese Patent Provisional Publication No. 128964/1987 and Japanese Patent Provisional Publication No. 226855/1987. The former Provisional Publication has disclosed a porcelain component containing, as the main component 25-80% by weight of SiO.sub.2, 15-70% by weight of either BaO or SrO, or both of them, and 1.5-5.0% by weight of B.sub.2 O.sub.3, and further 30% or less by weight of Al.sub.2 O.sub.3 if necessary, and adding any one of Cr.sub.2 O.sub.3, CuO, NiO, Co.sub.2 O.sub.3, and Fe.sub.2 O.sub.3, wherein when the additive is Cr.sub.2 O.sub.3 or CuO, it is added within the range of 0.2-10% by weight and when the additive is NiO, Co.sub.2 O.sub.3 or Fe.sub.2 O.sub.3, it is added within the range of 1-10% by weight.
These conventional porcelain components can be sintered in a non-oxidation environment at 1000.degree. C. and copper can be used as a conductor material.
However, the porcelain made of these conventional porcelain components has a dielectric constant .epsilon. of 6.1, Q-value of 1,400 (at 1 MHz) and a break-resistance force of about 1,600 Kg/cm.sup.2. Thus the Q-value is small and the break-resistance strength is weak.
Also, in order to increase the packaging density of an electric circuit substrate, it is necessary to internally contain cermet resistances. However, these conventional porcelain components have optimum baking temperatures ranging from 970.degree.-1000.degree. C., and resistance material such as cermet resistance can not be used at the baking temperature because of the high temperature. Further, an Inconel muffle is generally used as a material of a kiln, but its highest working temperature is said to be 1000.degree. C. and when it is always used at this temperature, deterioration of the kiln becomes severe.
Conventionally, it is known that the baking temperature can be decreased by adding alkali metal oxide such as Li.sub.2 O or Na.sub.2 O, or PbO for low temperature baking of the porcelain components, and generally technology has been proposed for decreasing the baking temperature by adding PbO as a glass component such as borosilicate lead.
However, in the above technology a large amount of the glass component such as borosilicate lead is added for decreasing the baking temperature and the break resistance force is improved, but the insulation resistance is impaired due to metallized deposition of PbO when a conductor material of the internal electrode such as copper is simultaneously baked in a non-oxidation environment.